1999 ML320 Substantial Fuel Leak - Mercedes-Benz Forum
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post #1 of 19 (permalink) Old 08-19-2014, 08:11 PM Thread Starter
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Date registered: Nov 2011
Vehicle: 1988 300E Factory 5 - Speed, 1990 300SEL, 1999 ML320, 2005 ML350, 1963 Corvette Roadster
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1999 ML320 Substantial Fuel Leak

Hello ,

On a recent trip my 1999 ML320 developed a major fuel leak in the rear of the car. The leak is only apparent when the car is running and shortly thereafter. It completely stops, apparently after fuel pressure is bled down.
I took out the drivers side wheel well, to expose the fuel filter and the fuel lines. I also took out the rear seat and lifted the carper to expose the top of the fuel tank and the hose connections. All appeared dry and not leaking. I started the car and there was again, a massive fuel leak. It was hard to trace the origin and appeared to be running down the tank from the area of the filler neck inlet. I question whether it is possible for the filler neck to only leak with the car running and the system under pressure. Additionally, I cant find the end of the small fuel line that runs from the fuel filter to somewhere on top of the tank in the area of the spare tire carrier. I see there are two large lines that run from the filter to the tank, as well as one large line that appears to run to the front of the car. Then there is a small, low pressure mystery line that comes off the filter to an unknown point over the fuel tank.
I replaced the fuel filter with an updated version and lines about 5 years ago without incident. Vehicle has been running fine to this point.
Any ideas? Does the mystery line go to a vent or canister that s clogged? Could the fuel filler neck be defective? Could it be one of the valves in the evap system?

The car has been giving an evap leak CEL for some time. Recently the low fuel light flashed rapidly with a 3/4 full fuel tank.

Thanks for your kind attention
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post #2 of 19 (permalink) Old 08-20-2014, 02:53 AM
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Remove the small panel door on the left side and have a look.
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post #3 of 19 (permalink) Old 08-20-2014, 12:20 PM Thread Starter
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Hi 43sqd,
Thanks for the suggestion. Unfortunatley, I opened my access panel and though I have the same valve / sensor, I don't have the fuel line plumbing that's apparent in your pic. My 1999, must be different than your 2002.
I'm going to try dropping the spare tire this evening to see if I can get a better look at things where the leak is apparent.
Thank you very much for your kind reply.
Out
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post #4 of 19 (permalink) Old 08-20-2014, 12:36 PM
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My experience with fuel leaking was from the fuel filter. The connector wasn't inserted properly & in time it got loose & slide back resulting in fuel leaking. Just like in your case it would leak while the engine is on & would stop shortly after switching off the car. I had to start the car & leave it running for a few minutes & get under, to see exactly were it was leaking from.

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post #5 of 19 (permalink) Old 08-20-2014, 01:20 PM Thread Starter
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Hi Art,
I appreciate your comment. When my leak occurred, I was actually hoping it would be a loose fuel line on the filter; because I could find it and fix it. Unfortunately, that isn’t my issue, as all is dry in that area while fuel rains down from above the tank to below when the engine is running.
I’m fairly sure this problem is linked to the evaporative system; that I just don’t understand well enough. Wondering what set of malfunctions could send gas through the system to be purged to the outside. Whatever evaporative calamity this system was set up to prevent has been multiplied tenfold by the spilling of gas from the system.
Thanks,
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post #6 of 19 (permalink) Old 08-20-2014, 01:39 PM
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This pic might help with the position of fuel lines.
1999 ML320 Substantial Fuel Leak-imageuploadedbyautoguide1408567128.710055.jpg
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post #7 of 19 (permalink) Old 08-20-2014, 02:40 PM Thread Starter
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MattML430,

YES!! This is pic is very helpful, thank you. I see there’s a lot more going on up there than I expected. More hoses, more opportunities for leaks. This validates my inclination to take out the spare tire carrier to get a better look at things.
Thanks very much!!
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post #8 of 19 (permalink) Old 08-20-2014, 08:39 PM Thread Starter
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Problem Solved; Maybe?
I removed the spare tire to get a better look at things on the top of the tank. Upon closer inspection, I found that the small mystery line from the fuel filter, AKA, fuel filter vent hose, is supposed to connect to the fuel tank just near the filler neck. Mine was not connected, as the short rubber hose connecting it was torn in half. Interestingly enough, in my further research, I stumbled on a post from 2010, titled; “Fuel leaking driver side rear tire” where a fellow with the same year ML, 1999, had the EXACT same problem; a tear in this small hose at the rear top of the tank. I also learned from this post that this vent hose should be dry; well mine is filled with fuel. Soooooooooo, I’m assuming I have two issues, the torn line that needs repair, as well as a bad fuel pressure regulator in the filter that needs replacing. I will try to get the parts tomorrow from the dealer and report results for reference by future fuel leakers.
Thanks,
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post #9 of 19 (permalink) Old 08-20-2014, 08:55 PM
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When my pressure regulator died in my fuel filter the small rubber hose was leaking fuel until the pressure bled off. The truck took longer to start and then I dug in and found the leak. Replaced the filter and all was well again.
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post #10 of 19 (permalink) Old 12-29-2016, 11:12 AM
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fuel filter to feed line

Thanks to the many previous posters in this and other posts about fuel leaks which really helped.
My ML has a fuel leak. It is hard to see in there even with the wheel well liner removed, but appears to be where the feed line connects to the filter. (see blue circle)
if/when i push up under the connector with a screwdriver the leak seems to worsen - i can see some actual drips. Filter has not been touched in 12 years (changed by dealer in 2005) so sort of unexpected finding.
Based on previous posts I was expecting the small vent line to have been leaking caused by defective pressure regulator. Just goes to show you should try to isolate source of a problem before buying parts.
I did connect my fuel pressure gauge to the fuel rail to see if it bounces (which it would expect to if the pressure regulator has failed) but gauge records zero psi with engine running so seems i must not have the correct fitting, would have been a nice datapoint to aid in decision making but ultimately I am planning on changing the filter anyway ( 163-477-07-01, note 07 not 05) and the feedline 163-470-28-64) to address the leak. Dealer can get both by tomorrow for 131 and 44 Cdn respectively plus tax, so seems the way to go.

Filter not overdue by miles (has 90kkm, ) but due soon i.e. due in 10 km, seems crazy to not just change it while changing the hose (presumably it is the hose that is the problem).
Hoping i can get by with not buying the special pliers as they are expensive and not readily available.

I am hoping once i disconnect both lines at the fuel pump I will be able to pull out the filter enough to access and disconnect the connectors at the filter with the pliers in the picture below (planned purchase).

point of the post; does my plan seem sound: new filter and feed line only? generic pliers? disconnect at pump and pull out assembly?
thanks.
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Last edited by Unhofliche_Gesundheit; 12-29-2016 at 11:16 AM.
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